Un-install RVM, Ruby, Ruby gem and rails in Ubuntu 12.04

rm -rf /usr/local/lib/ruby
rm -rf /usr/lib/ruby
rm -f /usr/local/bin/ruby
rm -f /usr/bin/ruby
rm -f /usr/local/bin/irb
rm -f /usr/bin/irb
rm -f /usr/local/bin/gem
rm -f /usr/bin/gem

 OR

You can use rm -rf ~/.rvm to remove RVM. 

If there is a separate version of ruby installed you'll need to 

sudo apt-get remove ruby1.x.x depending on the version